Process of recovering nitrous vapors or oxids of nitrogen diluted in indifferent gases.



P. A. GU 1E.

PROCESS OF REGOVERING NITROUS VAPORS 0R OXIDS 0F NITROGEN DILUTBD IN INDIPI'ERENT GASES.

APPLICATION FILED DEC. 15, 1910.

1 057 052 Patented Mar. 25, 1913.

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PHILIPPE AUGUSTE GU-YE,QOF GENEVA, SWITZERLAND.

rRocEss or RECOVERING m'rnous VALPORS on oxrns or NITROGEN DILUTED IN mmrrn'nnn'r eases.

Specification of Letters Patent.

, Application'flled December 15, 1910. Serial No. 597,535.

' Patented Mar. 25, 1913.

To all whom it may concern:

Be it known that I, PHILIPPE AUGUSTE GL'YE, citizen of the Republic of Switzerland, residing at Geneva, Switzerland, have invented new and useful Improvements in Processes of Recovering Nitrous Vapors or ()xids of Nitrogen Diluted in Indifferent Gases, of which the following is a specification.

The recovery of oxids of nitrogen diluted in a great excess of indifferent gases, such as are obtained, .for example, in the electrochemical manufacture of nitric acid by the action upon air of electric discharges (elec+ tric arcs or sparks), presents very great difiiculties in practice, attempts to overcome which have been made in recentyears by numerous improvements in the processes of absorption of the said-oxids of nitro en by water, sulfuric acid, alkaline liqui s, etc.

.These processes, however,.require costl installations, especially where the oxi s of nitrogen to be recovered are diluted with large amounts of indifferent gases.

.The present invention has for its object the direct recuperationof these dilute oxids of nitrogen, in the form of pure peroxid of nitrogen (N0 01' N 0 or of theperoxid mixed with other oxids of nitrogen (N 0 and ,NO), which are generally found in what is called dilute nitrous vapors; it was especially devised for treating the gases,

from furnaces for oxidizing nitrogen, but it is obviously applicable to all similar mixtures constituting nitrous vapors of any chemical origin.

The present invention is based, 1st, on the cooling of the gaseous mixture containing oxids of nitrogen, to a temperature sulficiently low to produce precipitation in liquid or solid form; 2nd, on the employment of the simple expansion of the gaseous mixture to produce the desired cooling, without attaining the temperature at which the indifl'erent gases would liquefy; 3rd, on the employment of apparatus for the expansion and exchange of temperature so as to'utilize as completely as possible, and with a minimum loss, all the cold produced bythe expansion.

The industry of; manufacturing liquefied gases has produced heat-interchangers-which operate with an efficiency of about 95%.

By making use of some such suitable heattemperature to minus 100 0. throughout the gaseous mass containin the oxids of nitrogen.. This lowering o. the temperature is suflicient to cause the precipitation of about W of the oxids of nitrogen diluted in the air in the proportion of 1% in volume-of gas,

NO. In very dilute nitrous vapors, there is a mixture of N 0 N0 N 0 and NO; all these gases are precipitated by cooling; in

particular, NO combines with N0 to give N 0,. The degree of cooling of the gases necessary to. produce the precipitation of NO can only e stated in a general way, be-

cause it depends upon the concentration of NO in the air. With pure NO the precipitation is complete at minus 14 degrees;

with gas containing about one percent. of

NO the temperature should be reduced to about 100 C. belowzero; for intermediate degrees of concentration, the temperature comes between the two stated limits. It may be said'that the cooling of the gases varies from minus 14 degrees C., to minus 100 degrees C., with concentration of NO varying from 100 per cent. to 1 per cent, if it is desired to recover the whole of the NO,.

If the mixture of gas to betreated contains a sufiicient excess of oxygen, the oxids of nitrogen being for the greater part in the form of N0 or N 0; (liquefying at about minus 14 (3.), the oxids of nitrogen 'will be deposited "in solid form, but if the oxids of nitrogen are also part-1y in. the form of N 0 (which liquefies at minus 82 0.), a liquid mixture of N 0 and N 0 will be obtained. In the first case, it will be advantageous to provide two heat interchangers in which the expansion of the gaseous mass to be treated will take place alternately; while one of said exchangers is operating, the solid peroxid of nitrogen -N. ,O in the other will be recuperated, either by letting it warm up until the solid peroxid liquefies, or by recovering said peroxid by Washing with a solvent of the peroxid N 0 which itself remains liquid at these low temperatures and the boiling point of which differs. sufiiciently from that of N 0, to enable the'N O, and the solvent to be easily separated afterward. All solvents (pureor interchanger. 'From this mixture the peroxid and the solvent are afterward separated by fractional distillation; the solvent is returned to the heat-interchanger apparatus. As asolvent suitable for the purpose may be mentioned here by way of example, the tetrachlorid of carbon, or a mixture of the same with chloroform or some saturated chlorated carbids, such aspentachlorethane, for instance.

It has been heretofore stated that a compression to 5 or 6 atmospheres followed by expansion in a heat interchanger to 1 atmosphere is suflicient, and I have found this degree of compression, followed by such ex pansion, tobe advantageous and economical, and lay claim thereto. In the other aspects of' the present invention, to wit, the introduction into the gases of a suitable solvent, such, for example, as those hereinbefore mentioned, and .in that aspect of the invention which relates to the utilization of divided carbon as hereinafter explained, I desire it understood that I do not limit the invention in such aspects to this degree of compression and expansion, nor do I limit this invention, exce )t in so far as it may be expressed in the c aims, to cooling by expansion or by compression and expansion. In such other aspects of my said invention compression to 5 or 6 atmospheres, followed by an expansion to 1 atmosphere, is suitable and desirable, but, as stated, I do not limit the invention in those aspects thereto. For instance, the compression might be carried to 15-18 atmospheres and the expansion take place to 3 atmospheres, the desired lowering of temperature being thus obtained. This methodof operation is especially advantageous if it is desired to produce as complete a precipitation as'possible of the oxids of nitrogen, which will be the case, for example, if the nitrous vapors to be treated are very much diluted in air. The previous compression of the gases issuing from the nitrogen-oxidizing furnaces also presents the advantage that this compression accelerates the transformation of the lower oxids into peroxid.. But the expansion may also be produced by lowering the pressure, from 1 atmosphere, for example. to a still lower pressure; in this case, the,

gaseous mixture to be treated, instead of being compressed before entering the heatinterchanger, will be drawn through said apparatus by a suitable suction ump, maintaining in said apparatus a su iciently low pressure. This method of operation is especially advantage0us if the gases issuing from the heat-interchanger apparatus must be returned into the nitrogen-oxidizing furnaces; for it is known from the works of Briner and Durand (Complies Rendus, vol. 145, page 248) that the output of these furnaces is appreciably increased when the gases therein are at a pressure of about 150 millimeters ofmercury.

If effective cooling means are available (a current of cold water, refrigerating machine, etc.) they may be used to' cool the gases before they are expanded; the greater the capacity of the cooling means, the less the work of the expansion. Even in the absence of cooling aneans, the proportion of the pressures between which the expansion takes place may be varied within large limits so as onlyto ,condenseall or part of the nitrous vapors.

The precipitation of the nitrous vapors may be accomplished by successive expansions, instead of by a single expansionfor example, the precipitation may be accomplished by an expansion of from 3 to 1 atmospheres followed by an-expansion of from 1 to atmospheres.

Divided carbon, preferably finely divided, (bone black, wood charcoal, coacoanut charcoal, etc.) may be introduced into the apparatus in which the condensation of the ox ids of nitrogen is effected by expansion. By reason of the well known property of this material of absorbing most gases, the condensation of the oxids of nitrogen can be effected at a temperature not so low as when the condensation is effected without the .intervention of the divided carbon, and consequently the proportion between the higher pressure and the lower pressure to be ado ted for the expansion may be smaller, which diminishes the mechanical work necessary to accomplish the condensation of the nitrous oxids. This manner of procedure may also be used in case there is introduced into the gases containing the nitrous oxids, in accordance with .the foregoing description, a liquid solvent difiicult to congeal. The condensation of the nitrous oxids being then accomplished at atemperature not so low, it sufiices that the liquid shall not eongeal at minus 25 C. For the final separation of the nitrous oxids this liquid (solvent) must boil at about plus 50 C. or higher.

The operation of the improved process is considerably simplified if gases free from moisture are used; in this case, all the apparatus (compressor, expander, exchanger) may be made of metal. If air is being used,

1,057,052 v I B it isalso an advantage to free it of carbonic anhydrid, which-precipitates partially with the oxids of nitrogen. These two conditions (elimination of water and carbonic a'nhydrid) are not, however, absolutely necessary. If the gases are humid, the apparatus will be constructed of or lined internally with some material not attacked by nitrous and nitric acids (stone-ware for example).

If the oxids ofnitrogen recovered contain a little carbonic. acid gas CO it is easily separable by distillation, inview of its great vo atility relatively to the oxids of nitro- The advantages of the new invention over previously proposed processes for recuperating nitrous vapors by cooling externally the apparatus through which pass the gases containing said vapors, are numerous. First,

the new invention presents a great simplification of apparatus; secondly, it results in a great saving of power relatively to the usual methods of cooling; thirdly, it may be combined veryadvantageously with the best methods for producing oxids of nitrogen, especially with those which are based u on the action of the electric arc in gases at ow pressure.

A suitable apparatus is diagrammatically shown in the accompanying drawing. In this drawing apparatus is shown organized to effect the 0001111 by compression and expansion, but, as be ore stated: my invention is not limited to this manner of cooling, nor

to such apparatus except as may be particularly specified in the clauses of'claim appended to this description.

In the said drawing C is a compressor. The gases drawn in at 1 are forced into the 40 conduit 2 at a pressure of 5 to 6 atmospheres, for instance, the pressure being indicated by the gage 3. The gases remain at that pressure in the apparatus as far as the valve 13. Before arriving atthe heat-inter- 46 changer D, the gases traverse a refrigerator R with outside circulation of cold water,

which enters at 4 and comes out at 4. Finally, through the injection tube 11, provided with a regulating valve 12, the sol- 50 vent for the nitrous vapors is introduced (chloroform for instance). The solvent is introduced under a ressure a little greater than that indicated y the pressure gage 3. The heat-interchanger is composed of sev- 56 eral cylindrical chambers concentrically arranged, four, for example, 5, 6-6, 77 and 88 At the lower part of the inner cylinder 5 there is a valve 13, re lated so as to open only under the operating pressure of 60 the compressor, indicated by the pressure gage 3, say, for instance, under a pressure of 5 or 6 atmospheres. The gases expand in the annular spaces 6-6, 77, 88, as the arrows indicate. By the cooling resulting from the expansion the nitrous vapors c0n 4 What I claim is 1. That improvement in a process forirecovering oxids of nitrogen diluted in a mixture of nitrogen 'and oxygen founded on the precipitation of the nitrous vapor by cold, 30 which consists in cooling the gases in the presence of a solvent having a congealing point lower than minus 50 C. and a boiling point above plus 50 (3., and,in separating the nitrous vaporsecondensed with the solg5 vent in the cooling apparatus.

2. The herein described process of recuperating nitrous vapors in' the presence of indiflt'erent gases less easily liquefiable than said nitrousvapors, which consists in compressing said gases to substantiallyfi atmos- Eheres and then introducing the same into a eat-interchanger wherein the same are.

cooled by expansion.

3. The herein described process of recu-- perating nitrous vapors in the presence of indifierentgases less easilyliquefiable than said nitrous vapors, which consists in causing the cooling of the gaseous mixture by expansion to produce precipitation of the nitrous vapors-without causing liquefaction .of the indiiferent gases, treating the precipitated nitrous vapors with a solvent which congeals only at temperatures below minus 50 C. and is volatile. only at temperatures above plus 50 C., and separating the solvent from the nitrous product by distillation.

4;. The herein described process of recuperating nitrous vapors in the presence of indifl'erent gases less easilyliquefiablethan said nitrous vapors, which involves cooling the gaseous mixture by expansion and the introduction to said gases of a small quantity of a solvent congealing below minus 50 0., and volatile above plus 50 C.

5. The herein described process ofrecu perating nitrous vapors in the presence of indifferent gases less easily liquefiable than said nitrous vapors, which consists in causing the cooling of the gaseous mixture by expansion, introducing into said mixture before'expansion a small quantity of a solvent congealing below minus 50 0., and volatile above plus 50 C., and separating the nitrous product 'from the solvent by distillation.

6. The herein described process of recuperating nitrous vapors in the presence of indiflerent gases less easily liquefiable than said nitrous vapors, which consists in causing the cooling of the gaseous mixture by ing the cooling of the'gaseous mixture by expansion, introducing into the gaseous lnixt'ure tetra chlorid of carbon and a chlorated carbid of the saturated series, and subsequently separating the solvent from the ni trous product by distillation.

S. The herein described process of recuperating nitrous vapors in the presence of indifierent gases less easily liquefiable than said nitrous vapors, which consists in causing the cooling of the gaseous mixture by expansion, introducing into the gaseous mix: ture carbon tetra chlorid and penta chlorethane, and subsequently separating the solvent from the nitrous product by distillation.

9. That step in a process of recovering, by cooling, nitrous vapors diluted in a mixture of nitrogen and. oxygen which consists in condensing the nitrog'en oxids in the presence of finely divided carbon.

10. That improvementin a process for recovery by cooling of the nitrous vapors diluted in a -1nixture of nitrogen and oxygen which consists in -arranging finely divided carbon in the apparatus for condensing the nitrogen oxids and adding to the gases containing the nitrogen oxids a liquid solvent for oxids of nitrogen not attacked by these nitrogen oxids, freezing below minus 25 C. and volatile above plus 50 C.

11. The herein described process of recuperating nitrous vapors in the presence of indifierent gases less easily liquefiable than said nitrous vapors, which consists in cooling the gaseous mixture by expansion in the presence of finely divided carbon.

12. The herein described process of recuperating nitrous vapors in the presence of indifierent gases less easily liquefiable than said nitrous vapors, which consists in adding to the gases a solvent congealing below minus 25 C. and volatile above plus 0., and expanding the gases in the presence of finely divided carbon.

In testimony whereof I have hereunto set my hand in presence of two subscribing witnesses.

, PHILIPPE AUGUSTE GUYE.

Witnesses:

L. H. MUNmR, C. VULLIE. 

